Draft
Outline

1. Introduction
2. The ONR-502 SPADUS Experiment
3. ADS Science and Design Philosophy
4. ADS Specifications and Design
5. Current Status for ADS
6. References

Summary

The Ancillary Diagnostic Sensor (ADS) portion of the SPADUS experiment (ONR 502) measures energetic electrons and nucleons above 15 keV and offers the unique opportunity to stay on the forefront of new science and technology at very low cost and risk while supporting the STP Advanced Research and Global Observation Satellite (ARGOS) related engineering and science.

ADS will provide a valuable spacecraft diagnostic capability and will likely give breakthrough scientific measurements by simultaneously measuring particle energy and intensity with high time resolution (20 ms) in two sensor modules. Although many particle sensors have previously flown in low-altitude orbit ADS opens up a new window of measurement capability (sensitivity, temporal resolution, predawn/postnoon orbit, association with new groundbased networks). In addition to pioneering new science and sensing the in situ low-altitude radiation belt the ADS objectives include obtaining fast spectral snapshots of Lightning- Induced Electron Precipitation (LEP) bursts and auroral pulsations and fine structure. ADS data may also be valuable for interpreting earth remote sensing data from the ARGOS NRL X-ray and UV imagers and from other low altitude satellites. The ADS sensor hardware has recently been included in the SPADUS digital box. Continued student participation in the development and subsequent data analysis offer unique educational opportunities.

ADS is currently accepted for flight on ARGOS by the appropriate management at the University of Chicago, the Space Test Program, The Aerospace Corporation, Rockwell, the Office of Naval Research and Taylor University. The spacecraft resources for ADS have been provided for and are included in the ICD: Power, mass, size, mounting, commands, telemetry, etc. No microprocessor system, DPU, LV power supply, telemetry board or mechanical box is required for ADS because the existing SPADUS digital electronics box contains the necessary space, power, and processing capability. The ADS hardware and GSE have recently been completed. This proposal requests modest funds to support documentation and testing.

1) Introduction

In the near-Earth space, both orbital debris and natural (cosmic) particles contribute to the particulate environment (Tuzzolino et al., 1992). The present-day lack of quantitative measurements of the flux, velocity / trajectory, and time characteristics of small debris particles continues to hamper the development of reliable evolutionary modeling of orbital debris, and the need for these data remains as an important goal in this field.

The SPAce DUSt (SPADUS) experiment addresses this need, providing important information on a) the orbital characteristics and possible sources of near-Earth cosmic dust and b) the mass distribution of meteor-stream particles which may be encountered. SPADUS is currently under development for launch on the STP Advanced Research and Global Observation Satellite (ARGOS) (figure 1) in Spring of 1997, and will be jointly developed by groups at The University of Chicago (dust sensors and linear electronics), the Lockheed Space Sciences Laboratory (digital electronics), and the Space Sciences Division of the Naval Research Laboratory (mechanical design and construction). SPADUS will be integrated and flown by the DOD Space Test Program. ARGOS is planned to be sun synchronous with a beta angle of 35 degrees and an altitude of 833 km. The ADS portion of SPADUS is a joint effort between Taylor University and the University of Chicago. We summarize the characteristics of SPADUS and the ARGOS mission.

2) The ONR-502 SPADUS Experiment

SPADUS is shown schematically in Figure 1. The main components are; A) a dust trajectory system, consisting of two identical planar arrays (D1 and D2) of polyvinylidene fluoride (PVDF) copolymer dust sensors, providing particle mass measurement, velocity (by time-of-flight), and trajectory measurement. B) a digital electronics box, which also contains an Ancillary Diagnostic Sensor (ADS) system for measurements of energetic electrons and nucleons, and C) an analog electronics box. A summary of the SPADUS characteristics is given in Table 1.

SPADUS Measurement Objectives

• To provide measurements of the mass, flux, velocity, and arrival direction of individual particles in near-Earth space, both for particles of natural origin (cosmic dust) and for man-made particles (orbital debris). Measurements will cover the particle diameter range ~ 2 mm to 200 mm.

• To provide an in situ map of the radiation-belt nucleon environment.

• To provide measurements of enhanced fluxes of energetic nucleons.

SPADUS Science Objectives

• DUST
  • To determine the trajectory for each incident cosmic dust particle and its likely source (comet, asteroid).

  • To search for transient dust flux increases from interplanetary dust stream encounters.

• ENERGETIC ELECTRONS and NUCLEONS
  • Study enhanced electron fluxes from lightning precipitation events.

  • Study enhanced nucleon fluxes from solar flare events.

SPADUS Engineering Objectives

• To obtain direct data on orbital and size distribution for small debris particles.

• To obtain data which will permit determination of hazards to critical surfaces and man in military and civil space programs.

• To provide continuous monitoring of the energetic electron and nucleon environment.

3) ADS Science, Technology, and Design Philosophy

The proposed ADS electron and ion particle telescopes are contained within the SPADUS digital electronics box. Even though many particle sensors have flown previously in low-earth polar orbit ADS will provide new measurements. To the best of our knowledge ADS will have unprecedented sensitivity and time coverage for energetic (E>15 keV) electrons and nucleons.

• To obtain fast spectral snapshots of Lightning-induced Electron Precipitation (LEP) events to better understand a major loss mechanism of the earth's radiation belts; The flux from an individual event can be of the order of 105 cm^-2 s^-1 sr^-1 from 50 to 1000 keV. The structure of the events can be studied for the first time with the ADS 20 ms time resolution. The LEP events can now be associated with the newly implemented lightning detection network and ground based VLF receiver network.

• To study enhanced fluxes from solar flares

• To provide a particle environment monitoring function for understanding backgrounds and energetic particle-induced anomalies on ARGOS.

• To obtain coordinated measurements with other ARGOS experiments. (No energetic particle detectors are on the ARGOS satellite) -Coordinate with the NRL UV and X-ray imagers. This is an opportunity to study the aurora with the NRL state-of-the-art UV imagers and measure for the first time the extent of LEP events with the high sensitivity X-ray imager (USA experiment).

• To coordinate measurements with other satellites to separate space-time ambiguities -ADS will measure the energetic particle spectrum at the foot of the field line (in situ flux and boundary measurements of the aurora) while the NASA POLAR satellite is recording aurora precipitation remotely. Multipoint measurements are essential to understanding the radiation belts. -Coordinated measurements with other satellite instruments may be essential for understanding spatial variations (e.g. the size of VLF duct regions )

• To pioneer NEW science with the ADS using the 20 ms fast spectra capability. The good time resolution and sensitivity will help to elucidate such phenomena as micropulsations, associated sudden commencement bursts of precipitation, trapping boundary structure, mid latitude chorus bursts, etc.

In addition to the science objectives there are important technology advancements that will be tested on ADS for future spaceflight instrumentation: analog-digital microchips and burst memory.

4) ADS Specifications and Design

Schematic Diagram	NEEDS MUCH MORE DESCRIPTION
The Si(Li) sensor module will measure the integral particle flux but with a 
detector area 10 times that of the S81-1 SEEP detectors.  The configuration and 
energy loss curves are shown in Figures 4 and 5.  Figure 6 shows the ADS 
telescopes mounted in the instrument box.  The SPADUS microprocessor (the 
SEPS type DPU)  will collect ADS data in a burst mode and store it on the 
SPADUS IO board in up to 16 Mb of EEPROM.  The ADS specifications are:	

5) Current Status for ADS

ADS is currently accepted for flight as a diagnostic sensor in SPADUS on the ARGOS satellite by the appropriate management at the University of Chicago, the Space Test Program, The Aerospace Corporation, Rockwell, and the Office of Naval Research. The Naval Research Laboratory strongly endorses the ADS sensor.

The spacecraft resources for ADS have been provided for and are included in the ICD: Power, mass, size, mounting, commands, telemetry, etc. ADS has been contained within the existing SPADUS digital box. ADS consist of two front end sensor modules with simple pulse height analysis. No microprocessor system, DPU, LV power supply, telemetry board or mechanical box is required for ADS because the SPADUS digital electronics box serves as the ADS interface.

6) References

Tuzzolino, A. J., J. A. Simpson, R. B. McKibben, H. D. Voss, and H. Gursky,  "An 
Instrument for Measurement of Orbital Debris and Natural Particles in Near-Earth 
Space," COSPAR-Spasce Debris, accepted for publication, 1992
 
Tuzzolino, A. J., J. A. Simpson, R. B. McKibben, H. D. Voss, and H. Gursky, "An 
LDEF II Dust Instrument for Discrimination Between Orbital Debris and Natural 
Particles in Near-Earth Space,"  Proc. Second LDEF Post-Ret. Sym., 1992

Voss, H. D., J. Mobilia, H. L. Collin, and W. L. Imhof, Satellite Observations and 
Instrumentation for Imaging Energetic Neutral Atoms," SPIE Conf., 1744, 1992

 Voss, H. D., J. R. Kilner, R. A. Baraze, J. Mobilia, R. B. Kash, A. Goodwater, and 
E. Kwok, "Analog/Digital VLSI Microcircuits for Spaceflight Applications, 
ìNASA Small Instrument Workshop, for publication, 1993